Characterization of water vapor transport in glassy polyacrylonitrile by combined permeation and sorption techniques

Diffusion time lags, steady state permeabilities and sorption/desorption kinetics are reported for water vapor in biaxially oriented, solvent cast polyacrylonitrile (PAN) films. A wide range of vapor activities was studied at 15°C, 30°C, and 45°C. The transient and steady state permeation behavior at low and intermediate upstream vapor activities suggests that Fickian transport occurs under most of the conditions studied. Specifically, time lags predicted by Fick's law using the concentration-dependent diffusion coefficient derived from steady state permeation measurements agree reasonably well with experimentally measured values in most cases. p]Integral sorption/desorption kinetics at low and intermediate vapor activities also appear to be Fickian with a concentration-dependent diffusion coefficient. The form of the concentration dependency, evaluated from the “long time” solution of the diffusion equation for sorption experiments, is consistent with the form established for the diffusion coefficient from the steady-state permeation data. The diffusion coefficient exhibits a maximum near the concentration at which clustering is initiated. Presumably, the effective diffusion coefficient of water increases initially due to plasticizing or dual mode sorption effects associated with gap filling in the glassy matrix. As clustering becomes significant, the effective mobility of water is substantially reduced; therefore, the diffusion coefficient decreases at higher activities as clustering becomes the dominant mode of sorption. p]A tendency of the “early time” sorption/desorption kinetic data to exhibit concavity to the square root time axis at high activities suggests that time-dependent reductions in the diffusion coefficient may be occurring. Such reductions could be related to the kinetics of cluster formation at the higher vapor activities during sorption and to slow polymer consolidation during desorption. Any such non-Fickian effects, related to chain segment relaxations occurring over time scales similar to those of a diffusional jump, appear to be of importance only at short times. The short time nature of any such processes is suggested by the fact that diffusion coefficients evaluated from the “long time” solution to the diffusion equation for sorption are consistent with coefficients evaluated from steady state permeation data, in which case all time-dependent relaxation phenomena should be absent.     

Iron(III) and ruthenium(II) porphyrin complex-catalyzed selective olefination of aldehydes with ethyl diazoacetate

The commercially available Fe(III) and Ru(II) porphyrin complexes Fe(TPP)Cl and Ru(TPP)(CO) are efficient catalysts for selective olefination of a variety of aldehydes with ethyl diazoacetate in the presence of triphenylphosphine. The reactions were carried out under mild conditions in a one-pot fashion with the use of a stoichiometrical amount of EDA, which proceeded with excellent yields and high (E)-selectivity. Air atmosphere, low catalyst loadings, and functional group tolerance were also demonstrated.     

PHOTOOXYGENATION OF MAGNESIUM meso-TETRAPHENYLPORPHYRIN*

Abstract— On unsensitized photooxygenation magnesium meso -tetraphenylporphyrin underwent oxidative ring cleavage yielding a bilitriene derivative as the sole product. Kinetic studies by quenching technique using singlet-oxygen quenchers, ß-carotene and α-tocopherol, and by substrate direct disappearance technique (Foote and Ching) indicated that only singlet-oxygen process is involved in the photooxygenation, and that the rate of total consumption of singlet oxygen ( k _Q+ k _R) is 1.0 ± 0.4 times 10⁸ M ^-1s^-1.     

Thermodynamics of Formation of Binary and Ternary Nitrides in the System Ce/Mn/N

Drop solution calorimetry in high‐temperature oxide melts has been shown to be very useful to study the energetics of nitride formation. This methodology was used to determine the enthalpies of formation from the elements of binary and ternary nitrides in the Ce/Mn/N system. The resulting values in kJ mol^–1 are; δH (CeN) = –340.19 ± 6.80, δ(H (Mn₃N_1.95, η‐Mn₃N₂ type) = –192.68 ± 7.57, δH (Mn₆N_5.40, θ‐Mn₆N₅ type) = –430.80 ± 10.93 and δH (Ce₂MnN₃) = –928.18 ± 9.46. The results show the role of inductive effects in Ce₂MnN₃ leading to a higher energetic stability compared to binary components.     

Eulerian–Lagrangian simulations of unsteady gas–liquid flows in bubble columns

We studied the dynamics of gas–liquid flows in a rectangular bubble column using Eulerian–Lagrangian simulations. Three-dimensional, unsteady simulations were performed to simulate the dynamic characteristics of the oscillating bubble plume. The effect of superficial gas velocity and aerated liquid height-to-column width (H/W) ratio on the dynamic and time-averaged flow properties was studied and the simulated results were validated using wall pressure and voidage fluctuation measurements. The effect of lift force and numerical diffusion on the dynamic and time-averaged properties is discussed in detail. Further, the results obtained using the Eulerian–Lagrangian simulations were compared with the Eulerian–Eulerian simulations. The bubble scale information, which is otherwise lost in the Eulerian–Eulerian simulations, was validated using the voidage fluctuation measurements. Such experimentally validated Eulerian–Lagrangian models will be useful for the simulation of mass transfer and reactions in bubble columns.